1. Field of the Invention
The present invention relates generally to a short-range communication system. In particular, in the dedicated short-range communication system, the present invention relates to a short-range communication apparatus which is destined to be mounted on a motor vehicle. More particularly, the present invention is concerned with a dedicated short-range communication on-vehicle apparatus which can be mounted or stuck on a windshield of a motor vehicle by making a mounting plate of the on-vehicle apparatus on the side for radiation of antenna from a radio wave transmissible material while adjusting the directivity of the antenna.
2. Description of Related Art
The dedicated short-range communication system (i.e., system dedicated for short-range communicator, also referred to as DSRC system for short) is designed for performing radio communication only within a limited range on a road by making use of radio wave of a microwave band. In such system, radio communication is carried out between an on-road apparatus (i.e., short-range communication apparatus installed on a road) and an on-vehicle apparatus (i.e., a short-range communication apparatus installed on a motor vehicle) for the purpose of transferring various types of data with a view to realizing such services as toll collection, presentation of traffic information and others, profitably for the drivers of motor vehicles and managers who are in charge of controlling of roads, parking spaces and others.
As the systems designed for performing such short-range communication, there have been conceived various and numerous applications such as exemplified by toll collections at gas stations, drive-throughs and the like and presentation of traffic information as well as the electronic toll collection (ETC for short), needless to say.
In the dedicated short-range communication system mentioned above, a dedicated short-range communication on-vehicle apparatus is mounted on the motor vehicle, which apparatus is designed for conducting short-range communication with road-side radio equipment installed on the road side through the medium of radio wave.
In general, the dedicated short-range communication on-vehicle apparatus employed in such dedicated short-range communication system is comprised of an antenna having the directivity in a predetermined direction, a radio module for performing transmission/reception of radio wave with road-side radio equipment through the antenna, and a data processing unit for processing the transmission/reception data transmitted/received by the radio module. As to the data processing unit among others, this unit has generally been combined integrally with a car navigation system installed in a dashboard of the motor vehicle in many applications. Of course, the motor vehicle must be then equipped with the car navigation system.
Heretofore, the dedicated short-range communication on-vehicle apparatus has been installed on a dashboard of the motor vehicle. However, the dedicated short-range communication on-vehicle apparatus mounted on the dashboard provides an obstacle to the view field. Besides, there exists a desire for making the dashboard aesthetically neat. For these reasons, there has been a demand for installing the dedicated short-range communication on-vehicle apparatus at another position.
Under the circumstances, such arrangement of the dedicated short-range communication on-vehicle apparatus has already been proposed that only the antenna or alternatively only the antenna and the radio module are mounted on the windshield of the motor vehicle. For more particular, reference may have to be made to Japanese Patent Application Laid-Open Publication No. 297758/1996 (JP-A-H8-27758), pp. 2 to 3, FIG. 3.
Further, as to the orientation (direction) of the directivity (boresight direction) of the antenna in the dedicated short-range communication on-vehicle apparatus, it is prescribed in the relevant mounting standards that the antenna should be directed with an angle of inclination in a range of 0 to 30 degrees (°) with reference to the forward direction of the motor vehicle, wherein the zenith direction is defined to be 0 degree with inclination in the forward direction being affixed with a sign “plus or +” while inclination in the backward direction is of a sign “minus or −”.
In conjunction with the dedicated short-range communication on-vehicle apparatus designed to be installed in combination with the car navigation system as mentioned previously, there has existed a demand for the apparatus of a unitary structure designed to realize only the functions of the dedicated short-range communication on-vehicle apparatus so that the dedicated short-range communication on-vehicle apparatus can also be employed in the motor vehicles which are not equipped with the car navigation system.
Certainly, the dedicated short-range communication on-vehicle apparatus of the type designed to be mounted optionally on the motor vehicle which is not equipped with the car navigation system has been implemented in the unitary structure which can be installed to be mounted on the dashboard of the motor vehicle, which apparatus however involves a problem mentioned below.
Namely, in the case where the dedicated short-range communication on-vehicle apparatus destined to be installed on the dashboard of the motor vehicle is stuck on the windshield as it is so that the view field is not obstructed, then the orientation (direction) of directivity of the antenna will incline excessively in the forward direction of the motor vehicle, rendering the on-vehicle apparatus useless because inclination of the windshield of the motor vehicle (direction normal to the windshield, e.g. 50 degrees (°) when the windshield plane is vertical as in the case of a four-wheel drive vehicle) is usually within the range of 25 degrees to 50 degrees.